Field of the Invention
The present invention relates to a magnetostrictive torque sensor having a plurality of detection coils for detecting a change in the magnetic characteristics of a magnetostrictive film disposed on an outer circumferential surface of a shaft. The present invention also relates to an electric power steering apparatus in which such a magnetostrictive torque sensor is incorporated.
Description of the Related Art
There have widely been used electric power steering apparatus, in which the steering torque of a steering wheel is detected by a magnetostrictive torque sensor, and energization of an electric motor is controlled on the basis of the detected steering torque in order to generate a steering assisting force.
In relation to magnetostrictive torque sensors of the above type, Japanese Laid-Open Patent Publication No. 2006-064445 discloses a technical concept concerning a magnetostrictive torque sensor having a shaft, a magnetostrictive film disposed on an outer circumferential surface of the shaft, and four detection coils juxtaposed along an axial direction of the shaft and disposed face-to-face with the magnetostrictive film. The detection coils detect a change in the magnetic characteristics of the magnetostrictive film, and a steering torque is calculated using a differential output (differential voltage) from the detection coils.